Generally, an excavator uses a rotational kinetic energy from the engine for minimizing an engine fuel loss in a working standby to discharge a working hydraulic oil through a main-line in a variable capacity pump of a main pump, returns the working hydraulic oil through the main-line to a tank through a bypass release pump when a main spool does not receive any signal through a neutral position port and transfers a pressure formed at an orifice to a pump regulator through a pump control line to control a tilting angle of the pump and to decrease a discharged flow.
Korean Patent Publication No. 10-2003-0056347 relates to the fuel economy and the pump for excavator minimum stream flow way of regulation letting enhance durability of the equipment the pump control including the modulation of the pump input horse power and pump inclined-angle etc, is done the power loss is minimized as to the excavator capable of the flow rate variable control of pump in the working standby. And the pump for excavator minimum stream flow way of regulation organizing the engine, the acceleration factor, the main control valve, the central control computer, the electronic proportion pressure reducing valve and solenoid valve in order to minimize the engine fuel loss in the working standby of the excavator and controls the minimum stream flow of pump and it adds the signal to the electronic proportion pressure reducing valve setting up the shuttle valve between the pilot line of the pilot pump controlled with the negative line and solenoid valve and operates the solenoid valve to the signal of the central control computer receiving the signal of the work standby state and the comparison senses the pressure in the shuttle valve and controls the pump regulator input torque at the central control computer operating the inclined-angle of pump to the minimum and receives the signal of the work standby state and controls the pump input torque to the minimum. According to a described technology, there are advantages that a power loss in an idle time can be minimized to reduce a fuel, improve an endurance and provide an environment-friendly construction equipment.
However, the excavator has disadvantages that engine revolution speed (for example, 2015 (rpm)) is increased in a driving time, a driving fuel consumption is increased and a driving noise is increased because only flow of a hydraulic pump is used as a driving power.